Rendering Glass (layers) resulting in strange dark patches (in Final but not Preview)
It looks like you have an object hidden in the viewport that is showing up in the render. 

Look for a setting in the outliner similar to this and either hide that object in the render or delete it:



Alternatively, you can press Alt+H, and you should see all hidden objects in the viewport. Then you can select and delete/disable anything you need to.

This script will automatically hide all objects in the render that are hidden in the viewport:

import bpy

for obj in bpy.context.scene.objects:
    if obj.hide and not obj.hide_render:
        obj.hide_render = True




Putting this here for reference...

Why does my object not show up?